This invention relates generally to the field of medical instrumentation and more specifically to spectroscopy instruments.
Spectroscopic applications for the medical field are proliferating rapidly and the need for a good white light source exists. Desirable characteristics of the white light source are that it should not produce too much heat and that it should be capable of being modulated.
Conventional white light sources, such as filament lamps, produce too much heat to be used in some medical applications such as tissue oximetry because of the heat they produce. Because the light source may need to be placed in close proximity to the patient, a high level of heat production is unacceptable.
For applications involving spectral analysis, a broadband light source is necessary which covers a wider spectral range than can be covered by a single LED. If several LED""s are used, then there are gaps between the wavelength coverage.
A solution to this problem is to utilize optical pumping of a luminescent compound such that the combination of pump wavelength and luminescent wavelengths combine to cover the wavelength range of interest. Luminescence includes both fluorescence, which is the relatively fast output, and phosphorescence, which is the relatively slow output. Typical fluorescence lifetimes are 10xe2x88x926 seconds, whereas phosphorescent lifetimes are in seconds.
A somewhat similar concept is currently being used to produce a xe2x80x9cwhite LEDxe2x80x9d flashlight, such as the ones marketed by Laserlyte of Torrance, Calif. In these flashlights, a bluish LED is used to pump a luminescent dye or compound such that the resultant output appears white to the eye. However, for spectroscopic applications, such as the tissue oximeter and others, the wavelength range of interest covers other regions, where current technology does not exist. Specifically, in the near infrared region, where tissue oximetry is important, such a xe2x80x9cquasi-whitexe2x80x9d LED does not exist. It is the purpose of this invention to describe the method and apparatus necessary to address this need. In this context, xe2x80x9cwhitexe2x80x9d means a relatively broad spectral bandwidth, and does not necessarily mean white to the eye. This could also be referred to as xe2x80x9cquasi-whitexe2x80x9d or xe2x80x9cbroadband near infraredxe2x80x9d, if in the near infrared region of the spectrum.
U.S. Pat. No. 5,998,925 (Shimiziu et al.) claims a light emitting diode (LED) with a nitride compound semiconductor and a phosphor with a garnet fluorescent material. However, the Shimiziu et al. LED is not well suited to be placed in close proximity to a patient to ensure substantial light entry into the patient, nor is it in the correct wavelength region to be of use for particular medical applications such as a tissue.
The present invention is a light source for a spectroscopy instrument. The light source, in a first embodiment, includes a light source and a block of translucent material. A luminescent material is formed within the block to pump the wavelength of the light source up to a desired range of wavelengths when the light source pumps light into the block. A surface opposite a tissue engaging surface of the block may be mirrored to reflect escaping light back into the patient. Other surfaces, except for a light receiving surface that receives light from the light source, may be metalized to further prevent light from escaping.
In a second embodiment, the spectroscopy light source includes a light source, a block and a light fiber for carrying light from the light source to the block. The light fiber is formed with the luminescent material to produce pumped light at the block.
The light source is preferably an LED, laser or a diode laser operating at 680 nm. The luminescent material preferably produces light in the range from 600 nm to 1000 nm. The luminescent material even more preferably produces light in the range from 720 nm to 850 nm when pumped by light at 680 nm.